The Impact of Bladder Filling on Patient Setup and Patient Time In the Treatment Room during Proton Therapy of Prostate Cancer Patients
Abstract
Purpose
The bladder is kept full during prostate proton therapy to push the small and large intestines out of the radiation field and maintain a consistent position for the bladder and nearby pelvic organs. However, it is a challenge to keep a regular bladder volume throughout the course of radiation, which may slow down treatment processes. This study aims to determine how bladder volume affects patient set-up, number of imaging episodes, and treatment durations.
Methods
In this retrospective analysis, data from 25 prostate cancer patients were analyzed. For each patient, a random five sessions of treatment were considered. For each session, the bladder volume, couch shifts, time in the treatment room, and number of KV and CBCT images were recorded. The net 3D Cartesian shift and percent volume difference from the planning volume were calculated for each treatment. Per-patient and pooled analysis was performed.
Results
The distribution of bladder volume difference at treatment is skewed towards underfilling (mean = 10.2, median = -3.03). Further, a negative correlation (r=-0.48) was found between the per-patient averaged volume differences and the planning volume. This suggests that patients who may have been underfilled at simulation will tend to have larger volumes at treatment, and vice versa. There is an expected correlation between the number of KV and CBCT images taken during patient setup and the treatment time (r=0.47). However, expected relationships between high volume differences and cartesian shift or treatment time are not readily apparent (r=0.14, r=0.06). Analysis is limited by outliers and corresponding factors, such as wait times for the shared beam facility across multiple rooms.
Conclusion
Current results show that patients may be presenting at simulation with bladder volumes inconsistent with those at treatments. Pooled correlations support that the relationship between bladder filling and patient setup is complex and warrants further investigation.